The 3-1 loss at St Mary's dealt a major blow to second-placed City's hopes of retaining their Premier League title.
"We had a great session on Wednesday afternoon and the feeling among the lads is very positive," said Zabaleta, quoted on City's official website.
"Sometimes after a game like Southampton you need a few days to think about what went wrong and why, and then come back stronger and I believe that's what will happen."
Zabaleta said: "We know we gave probably our worst performance for two years or more last Saturday and it couldn't have come at a worse time because it was such a vital game in the title race, and United keep winning so the gap is even bigger than before.
"But you never know in football."
Reflecting more on the Southampton game, the 28-year-old added: "I think it was just one of those days when everything went wrong.
"It's not an excuse, but sometimes when everyone is away for international duty in the days before it is difficult to prepare in the normal way, and I think it didn't help us on this occasion.
"But having said that, we must give full credit to Southampton, who played really well and pressed us from the first minute to the last.
"We have to hold our hands up and admit they were better than us on the day.
"We will learn from this defeat and use the deflated feeling we had afterwards as an inspiration to maybe try and re-discover the sort of spirit we had last season.
"We need to stand together, battle and show what we are really capable of.
"We will aim to get back to winning ways at the weekend in the FA Cup and that is our immediate focus now."